1. Field of the Invention
In some hazardous environments it is desirable or essential to protect personnel from the environmental hazards by supplying breathing air which has been filtered or purified to a sufficient extent to provide adequate respiratory protection.
One class of such device for providing this respiratory protection is based on head-wear such as a helmet or soft cap. The interior space between the head and the helmet shell or cap is arranged to be supplied with sufficiently pure air either by a built-in air filter and fan or by a remote pure air supply fed to the helmet interior by a suitable tube or pipe. The flow of filtered or purified air after going through the above-mentioned interior space, must be contained around the wearer's nose and mouth and this can be achieved by a suitable design of transparent full-face visor, advantageously that described in the above-identified application of Lowe and Odell.
In order to contain the purified airflow appropriately, the rear edges of the visor must be sufficiently sealed to the sides of the wearer's face to prevent unwanted escape of air. Once this sealing has been suitably effected the purified air, after passing over the wearer's nose and mouth, then escapes to atmosphere either via an unsealed gap at the lower edge of the visor or through a one-way exhaust valve if the visor-to-face sealing has been continued around the lower edge of the visor.
2. Description of the Prior Art
It is known for respiratory protective devices to be sealed against a wearer's face by sealing means comprising resilient strips of solid or foamed rubber or other elastomeric material. Such arrangements have required the sealing strip to be applied with substantial force against the wearer's face to form an effective seal and it has been found that varying forms of sealing member are necessary to accommodate a respirator to the widely differing head shapes for which it may be required.